JP3855800B2 - Image processing apparatus and image processing method - Google Patents

Image processing apparatus and image processing method Download PDF

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Publication number
JP3855800B2
JP3855800B2 JP2002051320A JP2002051320A JP3855800B2 JP 3855800 B2 JP3855800 B2 JP 3855800B2 JP 2002051320 A JP2002051320 A JP 2002051320A JP 2002051320 A JP2002051320 A JP 2002051320A JP 3855800 B2 JP3855800 B2 JP 3855800B2
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Prior art keywords
pixel
color
achromatic
image
data
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JP2003259135A (en
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敦 横地
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ブラザー工業株式会社
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    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04NPICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/46Colour picture communication systems
    • H04N1/56Processing of colour picture signals
    • H04N1/60Colour correction or control
    • H04N1/6072Colour correction or control adapting to different types of images, e.g. characters, graphs, black and white image portions

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to an image processing apparatus and an image processing method for determining whether or not each pixel of color image data is an achromatic color, and in particular, can eliminate a color shift and output a clear black character. The present invention relates to an image processing apparatus and an image processing method.
[0002]
[Prior art]
  An image processing apparatus that forms a color image, such as a color copier, includes a scanner that reads an image and an inkjet printer that prints the image read by the scanner. In general, a scanner is configured using a line sensor (reading device) such as a CCD or CIS. In a color copier that reproduces images in full color, a color image of a read original is color-separated and read line by line. The red, green, and blue image data read by the reading device is digitized and then digital data of three colors (cyan, magenta, yellow) or four colors (cyan, magenta, yellow, black). Converted to Ink jet printers are equipped with cyan, magenta, yellow or cyan, magenta, yellow, and black inks. Based on the converted data, the inks mounted on the ink jet printer are overprinted. As a result, the read image is reproduced.
[0003]
[Problems to be solved by the invention]
  However, when an image is read using a reading device such as a CCD or CIS, color misregistration occurs due to mechanical vibration, lens chromatic aberration, MTF difference, feeding accuracy, and the like. was there. The color image of the read document is read with color separation line by line. For example, if a displacement of the reading position occurs during reading of one pixel, the red, green, and blue image data to be obtained in one set is read. A part will shift. When red, green, and blue image data obtained in a shifted state is converted to digital data of three colors (four colors) for color reproduction, chromatic (color) ink is printed in the portion where the shifted data is reproduced. Smudge occurs. In particular, when color ink bleeds around black (characters), the character is unclear.
[0004]
  Further, the peripheral edge of the black character is not usually a black solid area, and the adjacent area is the background color (background color). For this reason, the character peripheral portion has a lighter color in terms of density. In particular, if the black character is thin, the character itself becomes a bright color. Therefore, there is a problem in that the black character of the read image is not read as black and the contrast of the character is lowered. Setting the output density standard (threshold) for the scanned data so that the brightly read black characters are output in high density black can improve the sharpness of the black characters, but it can express black gradation. There is a problem that the black spots in the low density region become conspicuous.
[0005]
  SUMMARY An advantage of some aspects of the invention is that it provides an image processing apparatus and an image processing method capable of eliminating a color shift and outputting a clear black image.
[0006]
[Means for Solving the Problems]
  In order to achieve this object, the image processing apparatus according to claim 1 determines whether or not each pixel is achromatic from color image data including a plurality of pixels including color signals of at least three colors. A determination pixel setting unit that uses a pixel having a minimum luminance component of the color signal as a determination pixel in a pixel region centered on the target pixel, and a determination pixel set by the determination pixel setting unitSaturation component of pixel area centered onAnd achromatic color determining means for determining whether or not the pixel of interest is an achromatic color.
[0007]
  According to the image processing apparatus of the first aspect, first, the determination pixel setting means sets the pixel having the minimum luminance component of the color signal as the determination pixel in the pixel region centered on the target pixel. . Then, the determination pixel set by the achromatic color determination meansSaturation component of pixel area centered onBased on the above, it is determined whether or not the target pixel is an achromatic color.
[0008]
  The image processing device according to claim 2 is the image processing device according to claim 1, wherein the achromatic color determination unit includes a pixel region centered on the determination pixel set by the determination pixel setting unit. Saturation average calculation means for calculating the average value of the saturation components is provided, and when the average value calculated by the saturation average calculation means is smaller than a predetermined threshold value, the target pixel is determined as an achromatic color pixel. To do.
[0009]
  According to the image processing apparatus of the second aspect, in addition to the same effect as the image processing apparatus of the first aspect, in the pixel region centered on the determination pixel set as the determination pixel by the determination pixel setting unit, The average value of the saturation components in the pixel area is calculated by the saturation average calculation means. If the calculated average value is smaller than a predetermined threshold value, the achromatic color determining means determines that the target pixel is an achromatic color pixel.
[0010]
  The image processing device according to claim 3 is the image processing device according to claim 2, further comprising: component conversion means for converting the color signal into a luminance component of a pixel and a plurality of saturation components, and the determination pixel setting The means sets a pixel having a minimum luminance component converted by the component conversion means as a determination pixel, and the saturation average calculation means includes a plurality of saturations converted by the component conversion means. The achromatic color discriminating means compares each calculated average value with a corresponding threshold value, and if the comparison results are all smaller than the threshold value, the attention value is calculated for each component. The pixel is determined as an achromatic pixel.
[0011]
  According to the image processing apparatus of the third aspect, the color signal is converted into a luminance component of the pixel and a plurality of saturation components by the component conversion means in addition to the same operation as the image processing apparatus of the second aspect. Is done. The pixel having the minimum luminance component converted by the component conversion unit is set as the determination pixel by the determination pixel setting unit. In addition, the average value is calculated for each of the plurality of saturation components by the saturation average calculation means, and the comparison results comparing each calculated average value with the corresponding threshold value are all smaller than the threshold value, The target pixel is determined to be an achromatic pixel by the achromatic color determining means.
[0012]
  An image processing apparatus according to a fourth aspect is the image processing apparatus according to any one of the first to third aspects, wherein the pixel area centered on the target pixel is a matrix area of 3 rows and 3 columns.
[0013]
  An image processing apparatus according to a fifth aspect is the image processing apparatus according to any one of the second to fourth aspects, wherein the pixel region centered on the determination pixel is configured by a matrix area of 3 rows and 3 columns.
[0014]
  The image processing device according to claim 6 is the image processing device according to any one of claims 1 to 5; color signal generation means for generating an image color signal indicating a color of a pixel of an output image from the color signal; An output means for outputting a signal generated by the color signal generation means, and causing the color signal generation means to generate an achromatic image color signal for a pixel determined to be an achromatic color by the achromatic color determination means. In addition, an achromatic color output means for outputting the generated image color signal to the output means is provided.
[0015]
  According to the image processing apparatus of the sixth aspect, the image color signal is generated from the color signal by the color signal generation means in addition to the same operation as the image processing apparatus according to any one of the first to fifth aspects. Here, the image color signal of the pixel determined as an achromatic color by the achromatic color determining means is generated as an achromatic image color signal by the color signal generating means in accordance with an instruction from the achromatic color output means. The generated image color signal is output by output means.
[0016]
  The image processing device according to claim 7 is the image processing device according to claim 6, wherein the achromatic color output unit includes a plurality of color signal values of pixels determined to be achromatic by the achromatic color determination unit. Color signal changing means for changing the color signal to the same value, and causing the color signal generating means to generate an achromatic image color signal based on the value of the color signal changed by the color signal changing means.
[0017]
  According to the image processing device of the seventh aspect, in addition to acting in the same manner as the image processing device according to the sixth aspect, the values of the plurality of color signals included in the pixels determined to be achromatic by the achromatic color determining means are: It is changed to the same value by the color signal changing means. Based on the value of the color signal changed by the color signal changing means, an achromatic image color signal is generated by the color signal generating means.
[0018]
  The image processing apparatus according to claim 8 is the image processing apparatus according to claim 6 or 7, wherein an edge detection unit that detects pixels in an edge portion of the image and a thin line detection unit that detects pixels in a thin line portion of the image. The achromatic color output means is a pixel detected as a fine line portion or an edge portion pixel by the edge detection means or the fine line detection means, and is determined as an achromatic color by the achromatic color determination means. For the pixels, the color signal generation means generates an achromatic image color signal.
[0019]
  According to the image processing apparatus of the eighth aspect, in addition to acting in the same manner as the image processing apparatus according to the sixth or seventh aspect, the pixels of the edge portion of the image are detected by the edge detection means. Further, the fine line detection means detects pixels in the fine line portion of the image. Here, if the pixel detected as the pixel of the thin line portion or the edge portion by the edge detection means or the thin line detection means is a pixel determined as an achromatic color by the achromatic color determination means, the image color signal is output as an achromatic color. According to the instruction of the means, the color signal generating means generates an achromatic image color signal.
[0020]
  The image processing apparatus according to claim 9 is the image processing apparatus according to any one of claims 6 to 8, wherein the achromatic image color signal instructed to the color signal generation means by the achromatic color output means is black. The image color signal.
[0021]
  The image processing method according to claim 10 is for determining whether or not each pixel is an achromatic color from color image data including a plurality of pixels including color signals of at least three colors. A determination pixel setting step in which a pixel having a minimum luminance component of the color signal in a pixel region centered on the pixel is set as a determination pixel, and a determination pixel set by the determination pixel setting stepSaturation component of pixel area centered onAnd an achromatic color determining step for determining whether or not the pixel of interest is an achromatic color.
[0022]
  According to the image processing method of the tenth aspect, first, in the determination pixel setting step, the pixel having the minimum luminance component of the color signal in the pixel region centered on the target pixel is set as the determination pixel. . Then, the determination pixel set by the achromatic color determination stepSaturation component of pixel area centered onBased on the above, it is determined whether or not the target pixel is an achromatic color.
[0023]
  The image processing method according to claim 11 is the image processing method according to claim 10, wherein the achromatic color determining step is performed in a pixel region centered on the determination pixel set by the determination pixel setting step. A saturation average calculation step for calculating an average value of saturation components is provided, and when the average value calculated by the saturation average calculation step is smaller than a predetermined threshold value, the target pixel is determined as an achromatic pixel. To do.
[0024]
  According to the image processing method of the eleventh aspect, in addition to the same operation as the image processing method according to the tenth aspect, in the pixel area centered on the determination pixel set by the determination pixel setting step, When the average value of the saturation components is calculated by the saturation average calculation step, and the calculated average value is smaller than a predetermined threshold value, the target pixel is determined to be an achromatic pixel by the achromatic color determination step. Is done.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a perspective view showing a color copier 1 as an image processing apparatus of the present invention.
[0026]
  The color copier 1 is provided with an operation panel 1b having a plurality of keys on the front surface of the main body 1a. The color copier 1 is operated by pressing a plurality of keys provided on the operation panel 1b. On the upper surface of the main body 1a, a document feeder 1e having a document insertion port 1c and a document discharge port 1d is provided. A document to be copied is inserted into the document insertion slot 1c with the document surface facing downward. The document inserted into the document insertion slot 1c is sent to the reading unit of the color copier 1 by the document feeder 1e, and the document image is a scanner (CCD line sensor 2, see FIG. 2) provided inside the copier. ) Is read out as image data and then discharged from the document discharge port 1d.
[0027]
  On the other hand, a lower portion of the main body 1a is provided with a paper feed tray 1f on which a plurality of recording sheets can be stacked and pulled out to the front. From the paper feed tray 1f, recording paper for printing the read image data is supplied into the main body 1a by driving a conveyance motor (LF motor) 102 (see FIG. 2) for conveying the recording paper. It has become.
[0028]
  Inside the main body 1a, an ink jet head (not shown) is provided at a position that becomes a facing surface (printing surface) of the supplied recording paper. An ink ejection surface having a plurality of nozzles is provided on the opposite surface side of the inkjet head on the recording paper side. To the inkjet head, four color inks of cyan, magenta, yellow, and black are supplied from an ink cartridge (not shown) filled with each ink. The ink supplied to the inkjet head is ejected from the ink ejection surface.
[0029]
  The inkjet head is mounted on a carriage (not shown) driven by a carriage motor (CR motor) 101 (see FIG. 2). The carriage is configured to move laterally with respect to the moving direction of the recording paper by driving a carriage (CR) motor 101, whereby the inkjet head is perpendicular to the moving direction of the recording paper. While moving in the direction, the data read as image data is printed on a recording sheet. The printed recording paper is discharged from a recording paper discharge port 1g provided on the side surface of the color copier 1.
[0030]
  FIG. 2 is a block diagram showing an outline of an electric circuit configuration of the color copier 1. The control device for controlling the color copier 1 includes a main body side control board 100 and a carriage board 120. The main body side control board 100 has a one-chip microcomputer (CPU) 91 and a ROM 92. A RAM 93, a line buffer 94, an RGB data conversion circuit 95, and a gate array (G / A) 96.
[0031]
  The CPU 91 as an arithmetic unit executes control of each process such as a document image reading process (image reading process, see FIG. 5) and a printing process in accordance with a control program stored in the ROM 92 in advance. Further, a print timing signal and a reset signal are generated, and each signal is transferred to a gate array 96 described later. An operation panel 1b is connected to the CPU 91, and each unit of the color copier 1 can be controlled in accordance with a user instruction from the operation panel 1b.
[0032]
  Further, the CPU 91 drives a driving circuit system of the color copying machine 1, that is, a CR motor driving circuit 101 a for driving the CR motor 101, an LF motor driving circuit 102 a for operating the LF motor 102, and a CCD motor 103. A CCD motor drive circuit 103a is connected. When a copy instruction is input from the operation panel 1b, the CPU 91 outputs a signal to the CCD motor drive circuit 103a as necessary to drive the CCD motor 103, thereby driving the CCD line sensor (scanner) 2. To scan the original image. Thereafter, signals are output to the CR motor driving circuit 101a and the LF motor driving circuit 102a at a predetermined timing, and the CR motor 101 and the LF motor 102 are operated to execute printing on the recording paper. The LF motor 102 is composed of a stepping motor, and is configured such that the number of rotations can be controlled by the number of pulses of the input pulse signal.
[0033]
  Further, the CPU 91 detects the paper sensor 105, the carriage origin position, and the CCD line sensor 2 origin position provided at predetermined positions for detecting the leading edge of the recording paper and the document position (size of the document), respectively. An origin sensor 106 or the like provided at a predetermined position is connected. The operation of each connected device is controlled by the CPU 91.
[0034]
  In addition, an analog / digital conversion circuit (A / D conversion circuit) 3 for converting analog data into digital data is connected to the CPU 91. The A / D conversion circuit 3 is connected to the CCD line sensor 2 and converts analog data of the document image input from the CCD line sensor 2 into digital data. The A / D conversion circuit 3 is a circuit that performs processing such as sampling, quantization, and binarization on input analog data to convert it into digital data. The converted digital data is input to the CPU 91 and written into a later-described RAM 93 by the CPU 91.
[0035]
  The CCD line sensor 2 is a device that receives the reflected light of the light irradiated on the document surface by the CCD, converts the received light into a charge amount by photoelectric conversion, and outputs it as an electrical signal. The CCD line sensor 2 is a line image sensor, and reads a document image line by line. The CCD line sensor 2 includes red (R), green (G), and blue (B) devices with a gap of several lines so that a color image of an original can be read. As a result, the read image (pixel) signal can be represented by three signal components of red (R), green (G), and blue (B), and the color of the original image can be represented by a color image. .
[0036]
  When the original image is read, the original or the CCD line sensor 2 moves while moving. As a result, the original image is read line by line by the CCD line sensor 2, and the three signals separated into red (R), green (G), and blue (B) are red data indicating red, respectively. , G data indicating green, and B data indicating blue (image (color) data, R, G, B data).
[0037]
  Here, since the red (R), green (G), and blue (B) devices have a gap of several lines, the data read at the same time is red (R), green (G), Different lines of the document are read for each color of blue (B). In other words, the three colors of data are aligned only when the devices of the respective colors scan the same line on the document. At this time, if a deviation occurs in the reading (reading position) due to the feeding accuracy or the like, the data at a different location for each color is read, and the color deviation occurs.
[0038]
  Thus, due to the characteristics of the CCD line sensor 2, color misregistration is likely to occur in a color copier equipped with a CCD line sensor. In particular, when this color misregistration occurs at the peripheral portion of a black image (black character, black thin line, edge), color ink blur occurs at the peripheral portion of the black character, thereby reducing the sharpness of the black character. However, since the color copier 1 of this embodiment includes the black character detection circuit 95a that corrects the color misregistration, the color misregistration that reduces the sharpness of the black characters can be eliminated.
[0039]
  The ROM 92 is a non-rewritable memory that stores control programs executed by the CPU 91, fixed values, and the like. The image reading processing program shown in FIG. 5 is stored in the ROM 92 as a part of the control program. The RAM 93 is a rewritable volatile memory for temporarily storing various data. The RAM 93 is provided with a buffer for temporarily storing image data (R, G, B data) read by the CCD line sensor 2 and then digitally converted by the A / D conversion circuit 3. The image data stored in this buffer is subjected to various corrections by image reading processing. As a result of the correction, the image data (each color data, that is, R data, G data, and B data) is supplied to the line buffer 94 at a 256 level value having a maximum intensity FFH and a minimum intensity 00H according to the signal intensity. Is written. The image data written to the line buffer 94 is erased from the buffer of the RAM 93.
[0040]
  The line buffer 94 is a memory for storing R, G, B data that has been subjected to various corrections by image reading processing. The image data (R, G, B data) read by the reading device (CCD line sensor 2) has a large amount of data, and the original image is read mechanically line by line while operating the reading device. Therefore, it takes time to read all the image data on the document surface. For this reason, if a series of processing for converting the read image data into print data is executed using the RAM 93, the capacity and the operation area of the RAM 93 are compressed. Therefore, the line buffer 94 is provided to secure the capacity of the RAM 93 by sequentially storing R, G, B data subjected to various corrections in a memory provided separately from the RAM 93. . Since the image data stored in the line buffer 94 is erased from the RAM 93, each process executed by the CPU 91 such as image data processing can be efficiently executed without squeezing the capacity of the RAM 93.
[0041]
  The R, G, and B data subjected to various corrections by the image reading process are stored in the line buffer 94 and then sequentially read from the line buffer 94 to the RGB data conversion circuit 95. Are converted into print data.
[0042]
  The RGB data conversion circuit 95 is a circuit for converting the read image data (R, G, B data) into print data (C, M, Ye, K data), and includes a black character detection circuit 95a. . Details of the black character detection circuit 95a will be described later.
[0043]
  As described above, printing by the color copier 1 of the present embodiment is performed by an inkjet method. In the ink jet method, a full color image is printed by overlapping and printing inks of cyan, magenta, yellow, and black. For this reason, the color indicated by the R, G, B data must be reproduced by mixing colors of cyan, magenta, yellow, and black. The print data (C, M, Ye, K data) includes cyan (C) by C data, magenta (M) by M data, yellow (Ye) by Ye data, and black (K) by K data. This is data for designating each discharge amount. Conversion from R, G, B data to C, M, Ye data is performed according to a direct map in which read colors R, G, B data and print colors C, M, Ye are associated with each other. The K data is added as print data by the black generation process (S15, see FIG. 8).
[0044]
  Although not shown, the RGB data conversion circuit 95 performs a black generation circuit (UCR) for performing the black generation process (S15), and performs image smoothing and edge enhancement (smoothing and edge). Circuit for emphasis processing (S12), recording gamma processing circuit for correcting printing characteristics of C, M, Ye, and K data based on the γ curve (recording γ processing (S16)), halftone processing (A binarization process (S17)) is provided.
[0045]
  Based on the print timing signal transferred from the CPU 91 and the print data transmitted from the RGB data conversion circuit 95, the gate array 96 prints the drive data on the recording medium, the drive signal, A synchronous transfer clock, a latch signal, a parameter signal for generating a basic print waveform signal, and an ejection timing signal output at a fixed period are output, and these signals are output to a carriage on which a head driver is mounted. Transfer to the substrate 120 side.
[0046]
  The carriage substrate 120 is a substrate for driving the inkjet head by a mounted head driver (drive circuit). The inkjet head and the head driver are connected by a flexible wiring board in which a copper foil wiring pattern is formed on a polyimide film having a thickness of 50 to 150 μm. This head driver is controlled via a gate array 96 mounted on the main body side control board 100, and applies a drive pulse having a waveform suitable for the recording mode to each drive element. Thereby, a predetermined amount of ink is ejected.
[0047]
  The CPU 91, the ROM 92, the RAM 93, the line buffer 94, the RGB data conversion circuit 95, and the gate array 96 are connected via a bus line 99. Each signal communicated between the carriage substrate 120 and the gate array 96 is transferred via a harness cable connecting the two.
[0048]
  FIG. 3 is a diagram showing the black character detection circuit 95a mounted on the main body side control board 100 of FIG. The black character detection circuit 95a is a circuit for detecting a black character in the image data and adding a black code indicating that to a pixel determined to be a black character. The black character detection circuit 95a includes a YIQ conversion circuit 95b, a fine line detection circuit 95c, an edge detection circuit 95d, an achromatic color region determination circuit 95e, and a black character determination circuit 95f.
[0049]
  The YIQ conversion circuit 95b is a circuit that converts R, G, B data read from the line buffer 94 into Y, I, Q data indicating luminance (Y) and saturation components (I, Q). Luminance (Y) is data indicating the brightness of the read image (pixel), and the smaller the value, the closer the density is (black). The saturation component (I, Q) is data represented by two components, the I component and the Q component, and has a hue (a chromatic color) as the value goes away from 0. It is data which shows. That is, the degree of achromatic color of the original R, G, B data can be known from the values of the Y, I, Q data.
[0050]
  The conversion from R, G, B data to Y, I, Q data is as follows: luminance (Y) = 0.3R data + 0.59G data + 0.11B data, and saturation (I) = R data−luminance ( Y), saturation (Q) = B data−luminance (Y).
[0051]
  The Y, I, and Q data converted by the YIQ conversion circuit 95b are input to the fine line detection circuit 95c, the edge detection circuit 95d, and the achromatic color region determination circuit 95e. The YIQ conversion circuit 95b reads image data (R, G, B data) of all pixels and converts them into Y, I, Q data. Here, the above-described RGB data conversion circuit 95 needs to perform smoothing and edge enhancement processing for performing image smoothing and edge enhancement based on Y, I, and Q data separately from black character determination. Therefore, the YIQ conversion circuit 95b outputs Y, I, and Q data not only to the thin line detection circuit 95c, the edge detection circuit 95d, and the achromatic color region determination circuit 95e, but also to a circuit that performs smoothing and edge enhancement processing.
[0052]
  The fine line detection circuit 95c is a circuit that detects a fine line portion in the image, and the edge detection circuit 95d is a circuit that detects an edge in the image. The edge detection circuit 95d performs edge detection using a Sobel filter. Here, the character often has a large amount of edge features or is composed of fine lines. Therefore, the fine line detection circuit 95c and the edge detection circuit 95d determine that the data detected as the fine line or the edge is a pixel in the character area.
[0053]
  Here, the image data of the edge portion and the thin line portion will be described with reference to FIG. FIG. 4 is a diagram showing an example of image data obtained when an image in which black characters are printed on a white background is read by the CCD line sensor 2, and each R, G, B data is obtained at an edge portion and a thin line portion. It is the figure which showed changing characteristically. In FIG. 4A, the image data of the edge portion is displayed. In FIG. 4A, three graphs 6 are displayed on the left side, and each graph 6r, 6g, 6b has R data indicating red signal intensity, G data indicating green signal intensity, The graph shows the B data indicating the blue signal intensity.
[0054]
  In the graph 6, the horizontal axis represents pixels (pixel X coordinates (X1) to (X5)), and the vertical axis represents signal intensity (00h to FFh). The change in the pixel signal intensity in the X-axis direction is shown in FIG. Show. The same position on the horizontal axis of the three graphs 6r, 6g, 6b is the data of the same (coordinate) pixel.
[0055]
  Displayed on the right side of each graph 6r, 6g, 6b is a table 7 showing the signal intensity of each color data corresponding to the graph as a numerical value for each pixel. In each table 7r, 7g, and 7b, the data of each pixel is displayed in association with XY coordinates (X1, Y1) to (X5, Y5) with the horizontal axis as the X coordinate and the vertical axis as the Y coordinate. Yes.
[0056]
  The data of the graphs 6r, 6g, and 6b are data of coordinates (X1, Y3) to (X5, Y3) surrounded by a thick frame in each table 7r, 7g, and 7b. As shown in the graphs 6r, 6g, and 6b and the tables 7r, 7g, and 7b, the levels of the R data, G data, and B data of the pixels are remarkably changed in the vicinity of the pixel with the X coordinate = (X3). It is shown. That is, the image data (signal intensity) that was in the vicinity of “FFH” at the coordinates (X1, Y3) to (X2, Y3) is “0” after the coordinates (X4, Y3). This change indicates that the pixels near the coordinates (X3, Y3) are the edges of the image.
[0057]
  Here, in the graphs 6r, 6g, and 6b, when attention is paid to the pixels (X3, Y3) in the vicinity of the edge, the signal intensity of each color data is different for each of R data, G data, and B data. That is, the pixel that should be black when R data = G data = B data = “0” has the values of G data = “12” and B data = “54”, so it does not become black. For this reason, the pixels that are black are up to the coordinate position of (X4, Y3), and the pixels (X3, Y3) are blurred (colored).
[0058]
  Also, in FIG. 4B, the image data of the thin line portion is shown as a graph 8 and a table 9 for each color data. In the graph 8, as in the graph 6 of the edge portion, the horizontal axis represents pixels (pixel X coordinates (X1) to (X5)), and the vertical axis represents signal intensity (00h to FFh). The change in intensity in the X-axis direction is shown. The same position on the horizontal axis of the three graphs 8r, 8g, 8b is the data of the same (coordinate) pixel.
[0059]
  In Table 9, which shows the signal intensity of each color data shown on the right side of each graph 8r, 8g, 8b, similarly to Table 7, the horizontal axis represents the X coordinate and the vertical axis represents the Y coordinate. Displayed in association with XY coordinates (X1, Y1) to (X5, Y5).
[0060]
  As shown in the graphs 8r, 8g, and 8b and the tables 9r, 9g, and 9b, the signal intensity is small in the vicinity of the X coordinate (X3), and the adjacent coordinates (X1, X2) of the X coordinate (X3) , X4, X5) indicates that the signal intensity is high (near “FFH”), that is, the pixel at coordinates (X3, Y3) is a thin line portion.
[0061]
  The G data has the minimum value in the pixels (X3, Y1) to (X3, Y5), but the minimum value of the R data is the pixels (X2, Y3) to (X3, Y3), B The minimum value of the data is pixels (X3, Y3) to (X4, Y3), which indicates that each color data is not read by the same pixel and has been shifted (occurrence of color shift). ). When R, G, B data is converted into print data in such a state, color blur occurs at the periphery of a black character (black image).
[0062]
  Returning to FIG. The achromatic color region determination circuit 95e is a circuit that determines whether or not a pixel is an achromatic color (black) from Y, I, and Q data indicating luminance (Y) and chroma components (I, Q). The black character determination circuit 95f is a circuit that determines whether or not a pixel determined to be a character region based on the determination results of the thin line detection circuit 95c and the edge detection circuit 95d is achromatic by the achromatic region determination circuit 95e. . The black character determination circuit 95f uses each pixel determined to be a character region as one target pixel 17 (see FIGS. 9 and 10), and a 3 × 3 pixel region 18 (FIG. 9, FIG. 9) centering on the target pixel 17. In FIG. 10, the pixel having the lowest luminance is extracted. The extracted pixel becomes the determination pixel 19 (see FIGS. 9 and 10), and a 3 × 3 pixel area centered on the determination pixel 19 is set as the determination area 20. If the average value of the saturation components (I, Q) in the determination area 20 is less than or equal to a predetermined threshold (below the first and second thresholds), the initially set target pixel 17 is an achromatic pixel. The circuit determines that the pixel is a chromatic color pixel if the threshold value is exceeded (see FIGS. 9 and 10).
[0063]
  This black character determination circuit 95f adds a black code for designating printing with black monochrome ink to the Y, I, and Q data of the pixel determined to be an achromatic pixel. Thereby, a series of processes for detecting a black character in the image data (determining whether or not the pixel is a black character) in the black character detection circuit 95a ends.
[0064]
  The black character determination circuit 95f determines that even a pixel that is not a character is an edge portion or a thin line portion as a character region, and performs the same processing. If this color misregistration occurs not only in characters but also in an achromatic (black) thin line portion or edge portion, the image sharpness is reduced. In such a case, the color misregistration is eliminated and the image sharpness is reduced. It can be improved.
[0065]
  Next, each process in the color copier 1 configured as described above will be described using the flowcharts of FIGS. 5 to 8 and the image data samples shown in FIGS. 9 and 10. FIG. 5 is a flowchart of the image reading process executed in the main body side control board 100. The image reading process is a process for executing correction of read data on image data (R, G, B data) converted into digital data by the A / D conversion circuit 3. In this image reading process, first, black correction (dark correction) is performed to correct the black level of the read image data by the black correction process (S1). Next, shading correction processing is executed (S2), and further reading γ processing for correcting the characteristics of the reading device (CCD line sensor 2) is executed (S3). Then, the read image data subjected to the characteristic correction of the reading optical system is written in the line buffer 94 by the processes of S1 to S3 (S4), and the image reading process is ended.
[0066]
  6 to 8 are flowcharts of processing executed by the RGB data conversion circuit 95. FIG. 6 prints the read image data (R, G, B data written to the line buffer 94 in the processing of S4). It is a flowchart of the RGB data conversion process which converts into data (C, M, Ye, K data). In this RGB data conversion processing, first, R, G, B data is read from the line buffer 94 and black character determination processing for extracting black character pixels from the image data is executed (S11), and then the read image data is smoothed. Smoothing and edge emphasis processing for performing emphasis and edge emphasis are executed (S12). Next, a YIQ reverse conversion process is performed to reverse-convert the R, G, B data converted into Y, I, Q data in the black character determination process (S11) from Y, I, Q data to R, G, B data. (S13) Then, direct map processing for converting the R, G, B data converted by the YIQ inverse conversion processing into print data (C, M, Ye data) based on the direct map is executed (S14).
[0067]
  The direct map is a table in which the color system (R, G, B) of the read image is associated with the color system (C, M, Ye) of the print image. Thereby, the correspondence between R, G, B data and C, M, Ye data is determined. Next, a black generation process for determining the discharge amount of black monochrome ink is executed (S15). Through this black generation process (S15) and the direct map process (S14), the ejection amounts of each ink, cyan (C), magenta (M), yellow (Ye), and black (K) at the time of printing are designated. Print data (C, M, Ye, K data) is created.
[0068]
  Then, a recording γ process is executed for correcting the color characteristics for each ink, cyan (C), magenta (M), yellow (Ye), and black (K) (correction of color characteristics for printing) (S16). In addition, a binarization process for performing halftone correction (such as dither diffusion) is executed (S17). Thereafter, print data (C, M, Ye, K data) of each pixel is transmitted to the gate array 96 (S18), and this RGB data conversion process is terminated.
[0069]
  FIG. 7 is a flowchart of the black character determination process (S11) executed in the RGB data conversion process. The black character determination process (S11) will be described with reference to FIGS. 9 and 10 schematically showing a data processing method using specific image data together with the flowchart of FIG.
[0070]
  The black character determination process (S11) is executed by the black character detection circuit 95a provided in the RGB data conversion circuit 95. In this black character determination process (S11), first, R, G, B data of each pixel is read from the line buffer 94 (S21). As an example, a 5 × 5 matrix of R, G, B data read out by the processing of S21 is shown in (FIG. 9A) and (FIG. 10A).
[0071]
  The read R, G, B data is converted into Y, I, Q data by the YIQ conversion circuit 95b (S22). The process of S22 is the YIQ conversion process shown in FIGS. 9B and 10B. Thereafter, the fine line detection circuit 95c executes a fine line detection process for detecting a fine line image (S23), and the edge detection circuit 95d executes an edge detection process for detecting an edge (S24). An area determined as a fine line or an edge based on the detection results of the fine line detection process (S23) and the edge detection process (S24) is set as a character area (S25). FIG. 9 shows Y, I, and Q data determined as edges in the process of S24. FIG. 10 also shows Y, I, and Q data determined to be thin lines in the process of S23.
[0072]
  Since the black character determination process is a process executed for pixels in the character area, an undetermined pixel in the character area is set as the target pixel 17 (S26). The processing after S26 will be described with reference to FIG. By the process of S26, the pixel (X3, Y3) is set as the target pixel 17 in FIG. Thereafter, a pixel having the minimum luminance value in the 3 × 3 matrix (pixel region 18) centered on the pixel of interest 17 is set as the determination pixel 19 (S27). If there are a plurality of pixels having the minimum luminance value, any one may be selected. For example, in FIG. 9B, the pixel of the coordinates (X4, Y2) that is first obtained when scanning is used, but other determination methods may be used. In FIG. 9B, the pixel (X4, Y2) having the minimum luminance is set as the determination pixel 19 in the 3 × 3 matrix (pixel area 18) centered on the pixel of interest 17 (X3, Y3).
[0073]
  Next, an average value of each of the saturation components (I, Q) is obtained in a 3 × 3 matrix centered on the determination pixel 19 (S28). In FIG. 9B, the average value of the determination region 20 centered on the determination pixel 19 (X4, Y2) is obtained for each of the saturation components (I, Q). Then, it is confirmed whether or not the calculated average value of the saturation component (I) is equal to or smaller than the first threshold value (S29). Here, the calculated average value of the saturation component (I) is the first value. If it is equal to or smaller than the threshold value (S29: Yes), it is further confirmed whether or not the calculated average value of the saturation component (Q) is equal to or smaller than the second threshold value (S30).
[0074]
  As a result, if the average value of the calculated saturation component (Q) is also equal to or smaller than the second threshold value (S30: Yes), the target pixel 17 is set as an achromatic pixel, and Y, I, and Q data of the pixel are displayed. The addition of the black code is designated (S31).
[0075]
  Thus, threshold values are provided for the saturation components (I, Q), respectively, and the first threshold value for the saturation components (I) is the saturation component (Q). Corresponds to the second threshold value. Then, when the average values of the calculated saturation components (I, Q) are smaller than the corresponding threshold values, the target pixel (the target pixel 17 in FIG. 9) is determined as an achromatic pixel. It is done.
[0076]
  The Y, I, and Q data are composed of three data. However, since the three data function as one image data, the black code corresponds to Y, I, Q corresponding to one pixel. One is added to the Q data.
[0077]
  In FIG. 9C, the average value 21 (illustrated by the black background color) of the saturation components (I, Q) for the determination pixel 19 is indicated by “−4” and “14”. The absolute values of the average value 21 of the saturation components (I, Q), that is, “4” and “14” are provided corresponding to the saturation components (I, Q), respectively. If it is smaller than the threshold value, the target pixel 17 is determined as an achromatic pixel.
[0078]
  Thereafter, in the black character determination process (S11), it is confirmed whether or not the determination of all the pixels in the character area is completed (S32). If the determination of all the pixels is completed (S32: Yes), this black character determination is performed. The process (S11) ends. On the other hand, as a result of checking in the process of S32, if the determination of all pixels is not completed (S32: No), the process proceeds to the process of S26, and the processes of S26 to S32 are performed until the determination of all pixels is completed. Execute repeatedly.
[0079]
  Further, as a result of checking in the process of S29, when the average value of the calculated saturation component (I) exceeds the first threshold value (S29: No), or the calculated saturation component (Q) If the average value exceeds the second threshold value (S30: No), the process proceeds to S32.
[0080]
  When a plurality of character areas are formed discontinuously in the image data, the black character determination process (S11) is sequentially executed for each character area. Then, in all the character areas, the determination is finished when all pixels in the character area are determined.
[0081]
  On the other hand, when it is determined that the line is a thin line in the process of S23, the process after the process S25 is executed similarly to the case where the edge is determined, and the target pixel 17 is set in the character area (S26) (FIG. 10). (B), coordinate (X3, Y3) reference). Then, in the Y, I, and Q data (FIG. 10B), the pixel area 18 centering on the target pixel 17 is selected, and the pixel (X3, Y2) having the minimum luminance in the pixel area 18 is determined. The pixel 19 is set (S27). If there are determination pixels having the same value (minimum luminance value), the smaller coordinate is selected as the determination pixel. Therefore, the pixel (X3, Y2) becomes the determination pixel 19.
[0082]
  Then, the average value of each of the saturation components (I, Q) is calculated in the pixel region (determination region 20) centered on this determination pixel (determination pixel 19) (S28). The calculated average value becomes the average value 21 of the determination pixel 19, and it is determined whether or not the pixel of interest 17 is an achromatic color based on whether or not the absolute value of the average value 21 is equal to or less than the first and second threshold values. (S29 to S31). As a result, the pixels determined to be achromatic in the thin line portion can be output in black ink as well as the edge portion.
[0083]
  In the black character determination process (S11) described above, the achromatic color determination of the target pixel is performed based on the average value of the saturation components of the pixels with the lowest luminance around the target pixel. In other words, even if color misregistration has occurred, the judgment criteria are shifted to the pixel with the smallest color overlap (minimum luminance), that is, the pixel that is less affected by color misregistration (highly reliable as the original document image color). Therefore, the effect of color misregistration can be reduced. For this reason, by performing the achromatic color determination of the pixel of interest by such a method, it is possible to correct the color shift and improve the sharpness of the output image.
[0084]
  The black code is added to the corresponding Y, I, Q data in the black character determination process (S11). The black code continues to be added to the corresponding data without being cleared even if the Y, I, Q data is converted to R, G, B data, or even print data (C, M, Ye data). Is done. As a result, it is possible to instruct printing of the pixels determined to be achromatic (black) in the black character determination process (S11) with black monochrome ink by the black generation process (S11).
[0085]
  FIG. 8 is a flowchart of the black generation process (S15) executed in the RGB data conversion process. The black generation process (S15) is executed by a black generation circuit (UCR) provided in the RGB data conversion circuit 95. In this black generation process (S15), first, it is confirmed whether or not there is print data to which a black code is added (C, M, Ye data of each pixel) (S41), and print data to which a black code is added. If there is (S41: Yes), the black data added C, M, Ye data is replaced with K data for instructing printing in black ink (S42), and this black generation process (S15) is terminated. To do. On the other hand, as a result of checking in the process of S41, if the print data is not black code added (S41: No), C ′, M ′, Ye ′, K ′ data is generated from the C, M, Ye data ( S43), this black generation process is terminated.
[0086]
  As described above, according to the color copying machine 1 of the present invention, even if color misregistration occurs in the read image data (black image area) due to the influence of the reading device or the like, this can be achieved. By eliminating this, it is possible to obtain a high-definition image from which color misregistration has been eliminated.
[0087]
  In the above embodiment, the determination pixel setting means described in claim 1 corresponds to the processing of S27 in the flowchart of FIG. The saturation average calculation means described in claim 2 corresponds to the processing of S28 in the flowchart of FIG. The color signal generating means according to claim 6 corresponds to the processing of S14 in the flowchart of FIG. The output means described in claim 6 corresponds to the processing of S18 in the flowchart of FIG. The achromatic color output means described in claim 6 corresponds to the processing of S42 in the flowchart of FIG.
[0088]
  Further, the achromatic color determining step according to claim 10 corresponds to the processes of S21 to S32 in the flowchart of FIG. The determination pixel setting step according to claim 10 corresponds to the processing of S27 in the flowchart of FIG. The saturation average calculation step according to claim 11 corresponds to the processing of S28 in the flowchart of FIG.
[0089]
  The present invention has been described above based on the embodiments. However, the present invention is not limited to the above-described embodiments, and various modifications and changes can be easily made without departing from the spirit of the present invention. Can be inferred.
[0090]
  For example, in this embodiment, the image data read by the CCD line sensor 2 is input from the A / D conversion circuit 3 to the CPU 91 and stored in the RAM 93. Instead, the image data is input from the A / D conversion circuit 3. It may be configured to input to the RGB data conversion circuit 95 via a port. According to this, a large amount of image data is not input to the CPU 91, and the control burden on the CPU 91 can be reduced.
[0091]
  In this embodiment, printing is performed with a single black ink only for pixels determined to be black. However, printing with a single black ink is performed not only for black but also for gray pixels. You may comprise as follows. According to this, even for a gray image in which color misregistration has occurred, the color blur from the edge can be eliminated, and a gray image with high definition can be obtained.
[0092]
  In this embodiment, the black code is directly added to the image data. Alternatively, the black code may be stored in association with the coordinates of the pixel. The read image can be reproduced by being managed by the coordinate position. That is, since each pixel is managed by coordinates, if a black code is stored in association with these coordinates, image data conversion processing (from Y, I, Q data to R, G, B data, and further C , M, Ye data), it is not necessary to determine the addition of the black code one by one, and the processing can be executed efficiently.
[0093]
  Further, in the above-described embodiment, the black code is added to instruct printing with a single black ink. Instead, the values of the R, G, B data of the pixels determined to be achromatic are changed. An achromatic color print data may be created by setting R data = G data = B data. In such a case, by setting R data = G data = B data = 0, black ink single color The printer may be configured to instruct printing with the printer. The process of setting the R, G, B data values of the pixels determined to be achromatic as R data = G data = B data corresponds to the color signal changing means according to claim 7.
[0094]
  Further, when R data = G data = B data, it may be aligned with the value of the pixel with the lowest signal value, or may be aligned with the average value of each signal value.
[0095]
  In addition, in the above embodiment, the achromatic color pixel is determined after executing the thin line detection process (S23) and the edge detection process (S24). Instead, the achromatic color pixel is determined. Later, the fine line detection process (S23) and the edge detection process (S24) may be executed or may be executed in parallel.
[0096]
【The invention's effect】
  According to the image processing apparatus of the first aspect, the determination pixel setting means sets the pixel having the minimum luminance component of the color signal as the determination pixel in the pixel region centered on the target pixel. Then, the determination pixel set by the achromatic color determination meansSaturation component of pixel area centered onBased on the above, it is determined whether or not the target pixel is an achromatic color. Since the value of the luminance component is a value that directly represents the degree of achromatic color of the pixel, it is possible to accurately determine the achromatic color pixel in the image by executing the achromatic color determination using such a value. There is an effect.
  Further, even if color misregistration occurs, the pixel with the most overlapping colors (the luminance component has the minimum value), that is, a pixel that is less affected by the color misregistration (highly reliable as the original document image color) By shifting the determination criteria to, and determining the achromatic color of the pixel of interest based on the saturation component of the pixel area centered on the determination pixel, it is possible to correct the color misregistration, and to make the output image sharpness There is an effect that can be improved.
[0097]
  According to the image processing apparatus of the second aspect, in addition to the effect produced by the image processing apparatus of the first aspect, in the pixel area centered on the determination pixel set by the determination pixel setting means, If the average value of the frequency components is smaller than a predetermined threshold value, it is possible to accurately determine the achromatic color pixel in the image by determining the target pixel as the achromatic color pixel by the achromatic color determining means. effective.
[0098]
  In general, when image processing is performed, due to the influence of a reading device or the like, a plurality of color signals originally possessed by a pixel (image) are not read corresponding to the pixel but are read out of alignment, and are essentially achromatic. A pixel (achromatic color pixel) may not be read as an achromatic color pixel (it will be read as a chromatic color pixel). However, in this apparatus, whether or not the target pixel is an achromatic color is not directly determined from the target pixel, and whether or not the target pixel is an achromatic pixel with the pixel having the lowest luminance around the target pixel as a determination pixel. Is determined. Therefore, the pixel with the most overlapping color signals, that is, the pixel with the smallest color shift and the closest color signal to the original pixel of interest can be selected as the determination pixel. Further, since the achromatic color pixel is determined based on the average value of the saturation components of the pixel region centered on the determination pixel, the color shift of the target pixel is corrected (subtracted), and the target pixel is ( It is possible to accurately determine whether the pixel is an achromatic pixel.
[0099]
  According to the image processing device of claim 3, in addition to the effect produced by the image processing device of claim 2, the color signal is converted into a luminance component of the pixel and a plurality of saturation components, and the converted luminance component is The pixel having the minimum value is set as the determination pixel. Further, when the average value is calculated for each of the plurality of saturation components by the saturation average calculation means, and the comparison results comparing the calculated average values with the corresponding threshold values are all smaller than the threshold values, The target pixel is determined as an achromatic pixel by the achromatic color determining means. Therefore, there is an effect that it is possible to strictly determine whether or not the target pixel is an achromatic pixel. In a color image, if an achromatic color pixel, particularly an achromatic color pixel having a high density, appears unintentionally due to a determination error, the influence on the image is significant. Therefore, the achromatic color pixel is strictly discriminated to prevent an achromatic color pixel from appearing unintentionally due to a determination error.
[0100]
  According to the image processing apparatus of the fourth aspect, in addition to the effect produced by the image processing apparatus according to any one of the first to third aspects, the pixel area centered on the target pixel is a matrix area of 3 rows and 3 columns. Composed. Therefore, since the pixel area for discriminating the achromatic color pixel is an appropriate area and can be set to the minimum pixel area, each process executed for discriminating the achromatic color can be performed efficiently. There is an effect that can be executed.
[0101]
  The matrix area of 3 rows and 3 columns centering on the target pixel is a minimum unit area that includes all pixels adjacent to the center of the target pixel. For this reason, since the minimum number of data can be collected uniformly from the area, the reliability of the calculated data (selection of the determination pixel) can be improved.
[0102]
  According to the image processing apparatus of the fifth aspect, in addition to the effect produced by the image processing apparatus according to any one of the second to fourth aspects, the pixel area centered on the determination pixel is a matrix area of 3 rows and 3 columns. Composed. Therefore, since the pixel area for discriminating the achromatic color pixel is an appropriate area and can be set to the minimum pixel area, each process executed for discriminating the achromatic color can be performed efficiently. There is an effect that can be executed.
[0103]
  The matrix area of 3 rows and 3 columns centering on the determination pixel is an area of a minimum unit including all pixels adjacent to the periphery of the determination pixel serving as the center. For this reason, since it is the minimum number of data from the area and the data can be collected evenly, there is an effect that the reliability of the calculated data (average value of the saturation component) can be improved. .
[0104]
  According to the image processing device of the sixth aspect, in addition to the effect produced by the image processing device according to any one of the first to fifth aspects, the color signal generating means generates the image color signal from the color signal. Here, the image color signal determined as an achromatic color pixel by the achromatic color determining means is generated as an achromatic image color signal by the color signal generating means. Then, the generated image color signal is output by the output means. Therefore, there is an effect that an achromatic image color signal can be generated and output to a pixel that is originally an achromatic color (achromatic pixel).
[0105]
  The output image is output to an appropriate device, for example, displayed on a display device such as a CRT, or printed on a sheet of paper using a recording device such as a printer, etc. (visual data is reproduced). Can do. Here, when an image color signal is simply generated from a color signal, if a color shift has occurred, pixels that are originally achromatic pixels (achromatic pixels) are not output in achromatic colors. If the achromatic color pixel is output as a chromatic color pixel at the periphery of the achromatic color image, the color image ink blurs at the periphery of the achromatic color image, and the sharpness of the achromatic color image is lowered. However, in this apparatus, the image color signal determined as an achromatic pixel by the achromatic color determining means can be output as an achromatic image color signal by the color signal generating means. Chromatic pixels) can be reproduced with an achromatic color, and an achromatic image with high definition can be obtained.
[0106]
  According to the image processing apparatus of the seventh aspect, in addition to the effect produced by the image processing apparatus of the sixth aspect, the color signal values of the plurality of color signals possessed by the pixels determined to be achromatic by the achromatic color determining means are changed. Change to the same value by means. Based on the value of the color signal changed by the color signal changing means, an achromatic image color signal is generated by the color signal generating means. Therefore, there is an effect that an achromatic image color signal can be generated accurately.
[0107]
  According to the image processing apparatus of the eighth aspect, in addition to the effect produced by the image processing apparatus of the sixth or seventh aspect, the edge detection unit detects pixels at the edge portion of the image. Further, the fine line detection means detects pixels in the fine line portion of the image. Here, if the pixel detected as the pixel of the thin line portion or the edge portion by the edge detection means or the thin line detection means is a pixel determined as an achromatic color by the achromatic color determination means, the image color signal is converted into a color signal generation means. To generate an achromatic image color signal. Therefore, there is an effect that the sharpness of the edge portion and the fine line portion of the image that greatly affects the image quality can be improved, and the image quality can be improved. In addition, since it is possible to perform discrimination of achromatic pixels by focusing on pixels of a fine line portion or an edge portion having a large influence on the image, it is possible to improve the image quality while efficiently executing the processing. There is an effect that can be done. Furthermore, since the thin line portion or the edge portion is often a character, it is possible to output a high-quality image in which the sharpness of the character (contrast with the background image) is ensured.
[0108]
  According to the image processing apparatus of the ninth aspect, in addition to the effect produced by the image processing apparatus according to any one of the sixth to eighth aspects, an achromatic image color instructed to the color signal generation means by the achromatic color output means The signal is a black image color signal. Therefore, there is an effect that the output of the black achromatic color pixel can be designated. A character image or the like is often black, and the black is not output as black (color shift or density reduction), thereby reducing the contrast and image quality of the character image. However, in this apparatus, when it is determined that the pixel is an achromatic pixel, it is possible to generate a black image color signal and specify that the pixel is output in black, so that the sharpness of the black pixel can be improved. There is an effect that can be done.
[0109]
  Further, for example, when forming a full color image by superimposing cyan, magenta, and yellow recording materials by an ink jet printer or the like, the black formed by superimposing the cyan, magenta, and yellow recording materials is the recording material. Due to its optical characteristics, it does not look completely black. However, in the instruction with the black image color signal, it is possible to instruct printing with a black monochrome recording material that does not use cyan, magenta, and yellow recording materials in addition to normal printing. For this reason, a black pixel can be made into complete black and a contrast can be improved.
[0110]
  According to the image processing method of the tenth aspect, in the determination pixel setting step, the pixel having the minimum luminance component of the color signal in the pixel region centered on the target pixel is set as the determination pixel. Then, the determination pixel set by the achromatic color determination stepSaturation component of pixel area centered onBased on the above, it is determined whether or not the target pixel is an achromatic color. Therefore, by executing each step, there is an effect that it is possible to accurately determine the achromatic pixel in the image.
[0111]
  According to the achromatic color discrimination method according to claim 11, in addition to the effect produced by the image processing method according to claim 10, the average value of the saturation components in the pixel area in the pixel area centered on the determination pixel is determined as saturation. When the average value calculated by the average calculation step is smaller than a predetermined threshold value, the target pixel is determined as an achromatic color pixel by the achromatic color determination step. Therefore, by executing each step, there is an effect that it is possible to accurately determine the achromatic pixel in the image.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a color copier according to an embodiment of the present invention.
FIG. 2 is a block diagram showing an outline of an electric circuit configuration of a color copier.
FIG. 3 is a block diagram showing an electrical configuration of a black character detection circuit of a color copier.
FIG. 4 is a diagram illustrating an example of image data obtained when a document image is read by a CCD line sensor.
FIG. 5 is a flowchart of image reading processing executed on the main body side control board.
FIG. 6 is a flowchart of RGB data conversion processing executed by the RGB data conversion circuit.
FIG. 7 is a flowchart of black character determination processing executed in the RGB data conversion processing.
FIG. 8 is a flowchart of black generation processing executed in RGB data conversion processing.
FIG. 9 is a diagram schematically illustrating a method of processing edge data using specific image data.
FIG. 10 is a diagram schematically showing a method of processing data of a thin line portion by specific image data.
[Explanation of symbols]
1 Color copier (image processing device)
95a Black character detection circuit (achromatic color discrimination means)
95b YIQ conversion circuit (component conversion means)
95c Fine line detection circuit (fine line detection means)
95d Edge detection circuit (edge detection means)

Claims (11)

  1. In an image processing apparatus for determining whether or not each pixel is an achromatic color image data consisting of a plurality of pixels including color signals of at least three colors,
    A determination pixel setting means for setting a pixel having a minimum luminance component of the color signal as a determination pixel in a pixel region centered on the target pixel;
    Achromatic color determining means for determining whether or not the pixel of interest is an achromatic color based on the saturation component of the pixel area centered on the determined pixel set by the determined pixel setting means. A featured image processing apparatus.
  2. The achromatic color determining means includes a saturation average calculating means for calculating an average value of saturation components in the pixel area in a pixel area centered on the determination pixel set by the determination pixel setting means,
    2. The image processing apparatus according to claim 1, wherein when the average value calculated by the saturation average calculation means is smaller than a predetermined threshold value, the target pixel is determined to be an achromatic color pixel. .
  3. Component conversion means for converting the color signal into a luminance component of the pixel and a plurality of saturation components;
    The determination pixel setting means sets a pixel whose luminance component converted by the component conversion means has a minimum value as a determination pixel.
    The saturation average calculation means calculates an average value for each of the plurality of saturation components converted by the component conversion means,
    The achromatic color determining means compares each calculated average value with a corresponding threshold value, and determines that the pixel of interest is an achromatic pixel when all the comparison results are smaller than the threshold value. The image processing apparatus according to claim 2.
  4.   The image processing apparatus according to claim 1, wherein the pixel region centered on the target pixel is configured by a matrix area of 3 rows and 3 columns.
  5.   5. The image processing apparatus according to claim 2, wherein the pixel region centered on the determination pixel is configured by a matrix area of 3 rows and 3 columns.
  6. Color signal generation means for generating an image color signal indicating the color of a pixel of an output image from the color signal;
    Output means for outputting the signal generated by the color signal generation means,
    An achromatic color output unit that causes the color signal generation unit to generate an achromatic image color signal and outputs the generated image color signal to the output unit for a pixel determined to be an achromatic color by the achromatic color determination unit. The image processing apparatus according to claim 1, further comprising:
  7. The achromatic color output means includes color signal changing means for changing the values of a plurality of color signals to the same value for pixels determined to be achromatic by the achromatic color determining means,
    7. The image processing apparatus according to claim 6, wherein the color signal generating means generates an achromatic image color signal based on the value of the color signal changed by the color signal changing means.
  8. Edge detection means for detecting pixels at the edge of the image;
    A fine line detecting means for detecting pixels in the fine line portion of the image,
    The achromatic color output means is a pixel detected as a pixel of a fine line part or an edge part by the edge detection means or the fine line detection means, and a pixel determined as an achromatic color by the achromatic color discrimination means, The image processing apparatus according to claim 6, wherein the color signal generation unit generates an achromatic image color signal.
  9.   The image processing apparatus according to claim 6, wherein the achromatic image color signal instructed by the achromatic color output unit to the color signal generation unit is a black image color signal.
  10. In an image processing method for determining whether or not each pixel is achromatic, color image data composed of a plurality of pixels including color signals of at least three colors,
    A determination pixel setting step in which a pixel having a minimum luminance component of the color signal in a pixel region centered on the target pixel is a determination pixel;
    An achromatic color determining step for determining whether or not the pixel of interest is an achromatic color based on a saturation component of a pixel region centered on the determined pixel set in the determination pixel setting step. A featured image processing method.
  11. The achromatic color determination step includes a saturation average calculation step of calculating an average value of saturation components in the pixel region in a pixel region centered on the determination pixel set by the determination pixel setting step,
    11. The image processing method according to claim 10, wherein when the average value calculated by the saturation average calculation step is smaller than a predetermined threshold value, the target pixel is determined as an achromatic pixel. .
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